Process for producing a diesel fuel stock from bitumen and synthesis gas

ABSTRACT

A process for producing a diesel fuel stock from bitumen uses steam, naphtha and a hydroisomerized diesel fraction produced by a gas conversion process, to respectively (i) stimulate the bitumen production, (ii) dilute it for pipeline transport to an upgrading facility, and (iii) increase the cetane number of a hydrotreated diesel fuel fraction produced by upgrading the bitumen by blending it with the hydroisomerized gas conversion diesel fraction, to form the diesel stock. This diesel stock has a higher cetane number than that produced from the bitumen alone, and is used for blending and forming diesel fuel.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The invention relates to a process for producing diesel fuel frombitumen and gas conversion. More particularly, the invention relates toa process in which a gas conversion process produces steam, naphtha anda diesel fraction, with the steam used for bitumen production, thenaphtha for bitumen pipelining and the bitumen converted to produce adiesel fraction. The two different diesel fractions are mixed to form adiesel fuel stock.

2. Background of the Invention

Very heavy crude oil deposits, such as the tar sand formations found inplaces like Canada and Venezuela, contain trillions of barrels of a veryheavy, viscous petroleum, commonly referred to as bitumen. The bitumenhas an API gravity typically in the range of from 5° to 10° and aviscosity, at formation temperatures and pressures that may be as highas a million centipoise. The hydrocarbonaceous molecules making up thebitumen are low in hydrogen and have a resin plus asphaltenes content ashigh as 70%. This makes the bitumen difficult to produce, transport andupgrade. Its viscosity must be reduced in-situ underground for it to bepumped out (produced), it needs to be diluted with a solvent if it is tobe transported by pipeline to an upgrading or other facility, and itshigh resin and asphaltene content tends to produce hydrocarbons low innormal paraffins. As a consequence, diesel fuel produced from bitumentends to be low in cetane number and a higher cetane hydrocarbon must beblended with it. Thus, producing a diesel fraction from bitumen requiresa plentiful supply of (i) steam, most of which is not recoverable, (ii)a diluent which can be used preferably on a once-through basis and (iii)a high cetane diesel fraction for blending with the low cetane bitumendiesel fraction.

A process for producing a diluent for transporting the bitumen upgradingfacilities by pipeline is disclosed, for example, in U.S. Pat. No.6,096,192.

Gas conversion processes, which produce hydrocarbons from a synthesisgas derived from natural gas, are well known. The synthesis gascomprises a mixture of H₂ and CO, which are reacted in the presence of aFischer-Tropsch catalyst to form hydrocarbons. Fixed bed, fluid bed andslurry hydrocarbon synthesis processes have been used, all of which arewell documented in various technical articles and in patents. Both lightand heavy hydrocarbons may synthesized, including low viscosity naphthafractions and diesel fractions relatively high in cetane number. Theseprocesses also produce steam and water. It would be an improvement tothe art if bitumen production and gas conversion could be integrated, toutilize products of the gas conversion process to enhance bitumenproduction and transportation, and to produce a diesel fraction having acetane number higher than a diesel fraction produced from the bitumen.

SUMMARY OF THE INVENTION

The invention relates to a process in which a hydrocarbon gas isconverted to a synthesis gas feed, from which liquid hydrocarbons,including naphtha and diesel fractions are synthesized and steam isgenerated, to facilitate bitumen production and transportation and toimprove the cetane number of diesel produced by upgrading the bitumen.The conversion of a hydrocarbon gas, and preferably natural gas tosynthesis gas, and the synthesis or production of hydrocarbons from thesynthesis gas will hereinafter be referred to as “gas conversion”. Theconversion of natural gas to synthesis gas and the synthesizing ofhydrocarbons from the synthesis gas are achieved by any suitablesynthesis gas and hydrocarbon synthesis processes. At least the higherboiling portion of the diesel fraction produced by the gas conversion ishydroisomerized to reduce its pour point, while preserving cetanenumber. The diesel fraction produced by the bitumen conversion ishydrotreated to reduce its heteroatom, aromatics and metals contents.The preferably natural gas used to produce the synthesis gas willtypically and preferably come from the bitumen field or a nearby gaswell. The synthesis gas is produced by any suitable process. The gasconversion process produces liquid hydrocarbons, including naphtha anddiesel fractions, steam and water. The steam is used to stimulate thebitumen production, the naphtha is used to dilute the bitumen fortransportation by pipeline to upgrading, and the higher cetane,hydroisomerized diesel is blended with the lower cetane bitumen diesel,to produce a diesel fuel stock. Thus, the invention broadly relates toan integrated gas conversion and bitumen production and upgradingprocess, in which gas conversion steam, naphtha and diesel fractionhydrocarbon liquids are respectively used to stimulate bitumenproduction, dilute the bitumen for pipelining and upgrade abitumen-derived diesel fraction.

Synthesis gas comprises a mixture of H₂ and CO and, in the process ofthe invention, it is contacted with a suitable hydrocarbon synthesiscatalyst, at reaction conditions effective for the H₂ and CO in the gasto react and produce hydrocarbons, at least a portion of which areliquid and include the naphtha and diesel fractions. It is preferredthat the synthesized hydrocarbons comprise mostly paraffinichydrocarbons, to produce a diesel fraction high in cetane number. Thismay be achieved by using a hydrocarbon synthesis catalyst comprising acobalt and/or ruthenium catalytic component, and preferably at leastcobalt. At least a portion of the gas conversion synthesized dieselfraction is upgraded by hydroisomerization to lower its pour and freezepoints. The higher boiling diesel hydrocarbons (e.g., 500-700° F.) arehighest in cetane number and are preferably hydroisomerized under mildconditions, to preserve the cetane number. The gas conversion portion ofthe process produces high and medium pressure steam, all or a portion ofwhich are injected into the ground to stimulate the bitumen production.Water is also produced by the hydrocarbon synthesis reaction, all or aportion of either or both of which may be heated to produce steam forthe bitumen production. Thus, by “gas conversion steam” or “steamobtained or derived from a gas conversion process” in the context of theinvention is meant to include any or all of the (i) high and mediumpressure steam produced by the gas conversion process and (ii) steamproduced from heating the hydrocarbon synthesis reaction water, and anycombination thereof. By bitumen production is meant steam stimulatedbitumen production, in which steam is injected down into a bitumenformation, to soften the bitumen and reduce its viscosity, so that itcan be pumped out of the ground. While the naphtha diluent may berecovered from the diluted bitumen after transportation, it is preferredthat the naphtha diluent be used on a once-through basis and not berecycled back to bitumen dilution. In another embodiment of theinvention, hydrogen is produced from the synthesis gas. This hydrogenmay be used for hydroisomerizing the gas conversion diesel fraction toreduce its pour point and, if the bitumen upgrading facility is close,for bitumen upgrading. The hydrocarbon synthesis reaction also producesa tail gas that contains methane and unreacted hydrogen. This tail gasmay be used as fuel to produce steam for bitumen production, boilerwater, pumps or other process utilities.

Upgrading bitumen in the process of the invention comprisesfractionation and two or more conversion operations, includinghydroconversion in which hydrogen is present as a reactant, to produceand upgrade the diesel fraction. By conversion is meant at least oneoperation in which at least a portion of the molecules is changed.Bitumen conversion comprises catalytic or non-catalytic cracking, andhydroprocessing operations such as hydrocracking, hydrotreating andhydroisomerization, in which hydrogen is a reactant. Coking is moretypically used for the cracking and cracks the bitumen into lowerboiling material and coke, without the presence of a catalyst. At leasta portion of these lower boiling hydrocarbons, including thehydrocarbons boiling in the diesel fuels range, are hydrotreated toreduce the amount of, heteroatoms (e.g., sulfur and nitrogen),aromatics, including condensed aromatics and metals that may be present.

The process of the invention briefly comprises (i) stimulating theproduction of bitumen with steam obtained from a hydrocarbon gas andpreferably a natural gas fed gas conversion process that producesnaphtha and diesel hydrocarbon fractions and steam, (ii) diluting theproduced bitumen with naphtha produced by the gas conversion to form apipelineable fluid mixture comprising the bitumen and diluent, (iii)transporting the mixture by pipeline to a bitumen upgrading facility,(iv) upgrading the bitumen to form lower boiling hydrocarbons, includinga diesel fraction, and (v) forming a mixture of the gas conversion andbitumen diesel fractions. In a more detailed embodiment the inventioncomprises the steps of (i) stimulating the production of bitumen withsteam obtained from a natural gas fed gas conversion process thatproduces naphtha and diesel hydrocarbon fractions and steam, (ii)treating at least a portion of the gas conversion diesel fraction toreduce its pour point, (iii) diluting the produced bitumen with naphthaproduced by the gas conversion, to form a pipelineable fluid mixturecomprising the bitumen and diluent and transporting the mixture bypipeline to a bitumen upgrading facility, (iv) upgrading the bitumen toform lower boiling hydrocarbons, including a diesel fraction and (v)treating the bitumen diesel fraction to reduce its sulfur content. Atleast a portion of both treated diesel fractions is combined to form adiesel stock having a cetane number higher than that of the treatedbitumen diesel fraction. In a still more detailed embodiment the processof the invention comprises:

(i) converting natural gas to a hot synthesis gas comprising a mixtureof H₂ and CO which is cooled by indirect heat exchange with water toproduce steam;

(ii) contacting the synthesis gas with a hydrocarbon synthesis catalystin one or more hydrocarbon synthesis reactors, at reaction conditionseffective for the H₂ and CO in the gas to react and produce heat, liquidhydrocarbons including naphtha and diesel fuel fractions, and a gascomprising methane and water vapor;

(iii) removing heat from the one or more reactors by indirect heatexchange with water to produce steam;

(iv) hydroisomerizing at least a portion of the diesel fraction formedin (ii) to reduce its pour point;

(v) passing at least a portion of the steam produced in either or bothsteps (i) and (iii) into a tar sand formation to heat soak and reducethe viscosity of the bitumen;

(vi) producing the bitumen by removing it from the formation;

(vii) reducing the viscosity of the produced bitumen by mixing it with adiluent comprising at least a portion of the naphtha produced in step(ii);

(viii) transporting the mixture by pipeline to a bitumen upgradingfacility;

(ix) upgrading the bitumen to lower boiling hydrocarbons, including adiesel fuel fraction containing heteroatom compounds;

(x) hydrotreating the bitumen diesel fuel fraction to reduce itsheteroatom content, and

(xi) combining at least a portion of the pour point reduced andhydrotreated diesel fuel fractions.

The hydrotreating also reduces the amount of unsaturated aromatic andmetal compounds. By bitumen diesel fraction, referred to above, is meanta diesel fuel fraction produced by upgrading the bitumen includingcoking and fractionation. The tar sand formation is preferably anunderground or subterranean formation having a drainage area penetratedwith at least one well, with the softened and viscosity-reduced bitumenproduced by removing it from the formation up through the well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simple block flow diagram of a process for producing bitumenand a diesel stock according to the invention.

FIG. 2 is a flow diagram of a gas conversion process useful in thepractice of the invention.

FIG. 3 is a block flow diagram of a bitumen upgrading process useful inthe practice of the invention.

DETAILED DESCRIPTION

The bitumen is produced from tar sand which is a term used to describe asandy, sedimentary rock formation that contains a bitumen-like, extraheavy oil in quantities large enough for it to be economically producedand refined into more useful, lower boiling products. In the process ofthe invention, high and/or medium pressure steam, respectively obtainedby cooling synthesis gas and the interior of the hydrocarbon synthesisreactor, is used to stimulate the bitumen production. The bitumenproduced from a tar sand formation or deposit is too viscous to betransported to an upgrading or refining facility by pipeline and musttherefore be diluted with a compatible and low viscosity liquid toenable it to be transported by pipeline. This requires a plentifulsupply of diluent, which it may not be economic to recover at theupgrading facility and recycle back to the bitumen production area fordilution again. The synergy of the process of the invention provides aplentiful and expendable supply of diluent for the bitumen pipelining.In the process of the invention, lower boiling liquid hydrocarbonsproduced by the gas conversion process are used as a diluent to decreasethe viscosity of the bitumen, so that it can be transported by pipeline.While the diluent may recovered and recycled back for bitumen dilutionprior to the bitumen conversion, it is preferred that it be used on aonce-through basis, to avoid the need for transporting it from thebitumen upgrading facility, back to the bitumen production well area. Bylower boiling is meant 700° F.−, preferably 600° F.−, more preferably500° F.−, and most preferably naphtha, including both light and heavynaphtha fractions, and mixtures thereof. A naphtha fraction has thelowest viscosity and may comprise hydrocarbons boiling in the range offrom C₅ up to as high as 420-450° F. Heavy naphtha may have a boilingrange of from 270-420/450° F., while for a light naphtha it is typicallyC₅-320° F. When maximum diesel production is desired, at least all ofthe 500° F.+ cetane-richest diesel fraction produced by the gasconversion will be blended with the hydrotreated diesel fractionproduced by bitumen conversion, and not used as diluent. This avoidscontaminating the gas conversion diesel with the metal and heteroatomcompounds in the bitumen, and the subsequent hydrotreating required bysuch contamination, since diesel produced by gas conversion does notrequire hydrotreating for metals, aromatics and heteroatom removal. Thatis, if the cetane-rich gas conversion diesel is used as part of thediluent and recovered during the bitumen upgrading, it will have to behydrotreated due to the contamination from the bitumen. To preserve thecetane number, this hydrotreating must be less severe than that used forthe diesel produced by the bitumen conversion and will therefore requirea separate hydrotreating reactor and associated facilities.

Upgrading bitumen comprises fractionation and one or more conversionoperations in which at least a portion of the molecular structure ischanged, with or without the presence of hydrogen and/or a catalyst.These conversion operations include cracking the bitumen to lowerboiling fractions. This cracking may be either catalytic ornon-catalytic (coking) cracking. Coking is typically used and convertsmost of the about 1000° F.+ bitumen to lower boiling hydrocarbons andcoke. Partial hydroprocessing may precede cracking, but this is notpreferred in the practice of the invention. The lower boilinghydrocarbons produced by coking, including diesel fractions, are treatedby reacting with hydrogen to remove heteroatom compounds, unsaturatedaromatics and metal compounds, as well as add hydrogen to the molecules.This requires a good supply of hydrogen, because these lower boilinghydrocarbons are high in heteroatom compounds (e.g., sulfur), and have alow hydrogen to carbon ratio (e.g., ˜1.4-1.8). If the bitumen upgradingfacility is close enough to the gas conversion operation, all or aportion of the hydrogen for upgrading may be obtained from the synthesisgas produced in the gas conversion portion of the process. Theintegrated process of the invention, which produces the bitumen diluent,eliminates the need for catalytic hydroconversion of the bitumen toreduce its viscosity before it is diluted and pipelined, that theprocess disclosed in the '192 patent requires.

Liquid products, such as diesel fractions, resulting from upgradingbitumen are low in normal paraffins. As a consequence, the cetane numberof diesel fractions recovered from bitumen upgrading typically rangesfrom between about 35-45. While this may be sufficient for a heavy dutyroad diesel fuel, it is lower than desired for other diesel fuels. Thebitumen-derived diesel fractions are therefore blended with dieselfractions having a higher cetane number. Bitumen diesel fractionsproduced by coking the bitumen are hydrotreated to remove aromatics andmetals and heteroatom compounds such as sulfur and nitrogen, to producea treated diesel fraction useful as a blending stock. The higher cetanenumber diesel fraction produced from the gas conversion process isblended with one or more treated diesel fractions, to produce dieselfuel stocks. Diesel fuel is produced by forming an admixture of asuitable additive package and a diesel fuel stock. The term“hydrotreating” as used herein refers to processes wherein hydrogen orhydrogen in a hydrogen-containing treat gas reacts with a feed in thepresence of one or more catalysts active for the removal of heteroatoms(such as sulfur and nitrogen), metals, saturation of aromatics and,optionally, saturation of aliphatic unsaturates. Such hydrotreatingcatalysts include any conventional hydrotreating catalyst, such ascomprising at least one Group VIII metal catalytic component, preferablyat least one of Fe, Co and Ni, and preferably at least one Group VImetal catalytic component, preferably Mo and W, on a high surface areasupport material, such as alumina, silica and silica-alumina. Othersuitable hydrotreating catalysts include zeolitic components.Hydrotreating conditions are well known and include temperatures andpressures up to about 450° C. and 3,000 psig, depending on the feed andcatalyst.

The natural gas used to produce the synthesis gas will typically andpreferably come from the bitumen field or a nearby gas well. Plentifulsupplies of natural gas are typically found in or nearby tar sandformations. The high methane content of natural gas makes it an idealnatural fuel for producing synthesis gas. It is not unusual for naturalgas to comprise as much as 92+ mole % methane, with the remainder beingprimarily C₂₊ hydrocarbons, nitrogen and CO₂. Thus, it is an ideal andrelatively clean fuel for synthesis gas production and plentiful amountsare typically found associated with or nearby tar sand formations. Ifnecessary, heteroatom compounds (particularly HCN, NH₃ and sulfur) areremoved to form a clean synthesis gas, which is then passed into ahydrocarbon synthesis gas reactor. While C₂-C₅ hydrocarbons present inthe gas may be left in for synthesis gas production, they are typicallyseparated for LPG, while the C₅₊ hydrocarbons are condensed out and areknown as gas well condensate. The methane-rich gas remaining afterseparation of the higher hydrocarbons, sulfur and heteroatom compounds,and in some cases also nitrogen and CO₂, is passed as fuel into asynthesis gas generator. Known processes for synthesis gas productioninclude partial oxidation, catalytic steam reforming, water gas shiftreaction and combination thereof. These processes include gas phasepartial oxidation (GPOX), autothermal reforming (ATR), fluid bedsynthesis gas generation (FBSG), partial oxidation (POX), catalyticpartial oxidation (CPO), and steam reforming. ATR and FBSG employpartial oxidation and catalytic steam reforming. A review of theseprocesses and their relative merits may be found, for example, in U.S.Pat. No. 5,883,138. Synthesis gas processes are highly exothermic and itis not uncommon for the synthesis gas exiting the reactor to be, forexample, at a temperature as high as 2000° F. and at a pressure of 50atmospheres. The hot synthesis gas exiting the reactor is cooled byindirect heat exchange with water. This produces a substantial amount ofhigh pressure (e.g., 600-900/2000 psia) steam at respective temperaturesof about 490-535/635-700° F., which may be heated even further. Thissteam may be passed down into a tar sand formation, with compression ifnecessary, to heat, soften and reduce the viscosity of the bitumen, andthereby stimulate the bitumen production. Both the synthesis gas andhydrocarbon production reactions are highly exothermic. Water used tocool the hydrocarbon synthesis reactor typically produces mediumpressure steam and this may be used for bitumen production or otheroperations in the overall process of the invention.

The synthesis gas, after cleanup if necessary, is passed into ahydrocarbon synthesis reactor in which the H₂ and CO react in thepresence of a Fischer-Tropsch type of catalyst to produce hydrocarbons,including light and heavy fractions. The light (e.g., 700° F.−) fractioncontains hydrocarbons boiling in the naphtha and diesel fuel ranges. Anaphtha fraction has the lowest viscosity and may comprise hydrocarbonsboiling in the range of from C₅ up to as high as 420-450° F. Heavynaphtha may have a boiling range of from 270-420/450° F., while for alight naphtha it is typically C₅-320° F. The lighter naphtha fractionhas a lower viscosity than the broad or heavy fractions. Dilutionexperiments were conducted by diluting a Cold Lake bitumen with C₅-250°F. naphtha and with a 250-700° F. middle distillate fraction, both ofwhich were produced in a Fischer-Tropsch hydrocarbon synthesis reactor.It was found that 31 vol. % of the naphtha was required to reduce theviscosity of the bitumen to 40 cSt @ 40° C. In contrast, 40 vol. % ofthe distillate fraction and 38 vol. % of the prior art gas condensatediluent were respectively required to reduce the viscosity. Thus,diluting bitumen with gas conversion naphtha requires significantly lessdiluent than when using a gas well condensate as the diluent. A dieselfuel fraction may boil within and including a range as broad as 250-700°F., with from 350-650° F. preferred for some applications. A 500-700° F.diesel fuel fraction produced by the gas conversion has the highestcetane number, pour point and freeze point, while the lighter, ˜500° F.−portion is relatively higher in oxygenates, which impart good lubricityto the diesel fuel. Hydroisomerizing the lighter diesel material willremove the oxygenates, while hydroisomerizing the higher material toreduce its pour and freeze points may reduce the cetane number.Therefore, at least the 500-700° F. diesel fraction produced by thesynthesis gas is mildly hydroisomerized to reduce its pour point, whileminimizing reduction in cetane number. Mild hydroisomerization istypically achieved under conditions of temperature and pressure of fromabout 100-1500 psig and 500-850° F. This is known and disclosed in, forexample, U.S. Pat. No. 5,689,031 the disclosure of which is incorporatedherein by reference. The cetane number of a diesel fraction produced bya Fischer-Tropsch gas conversion process hydrocarbon product may, aftermild hydroisomerization, be 65-75+, with most of the high cetanematerial present in the higher boiling, 500-700° F. hydrocarbons. Whenmaximum diesel production is desired, all or most of the gas conversiondiesel fraction, and at least the cetane-rich heavier diesel fraction(e.g., 500/550-700° F.) produced by the gas conversion, will be blendedwith a hydrotreated diesel fraction produced from the bitumen.

The table below illustrates a typical hydrocarbon product distribution,by boiling range, of a slurry Fischer-Tropsch hydrocarbon synthesisreactor employing a catalyst comprising a cobalt catalytic component ona titania-containing silica and alumina support component.

Wt. % Product Distribution from Slurry Hydrocarbon Synthesis ReactorIBP(C₅)-320° F. 13 320-500° F. 23 500-700° F. 19  700-1050° F. 34 1050°F.+ 11

As the data in the table show, the light naphtha fraction is 13 wt. % ofthe total hydrocarbon synthesis reactor product. The overall dieselfraction is greater than 42 wt. %. The 500-700° F. high cetane fractionis 19 wt. % of the total product, or more than 45 wt. % of the totalpossible diesel fraction. While not shown, the total (C₅-400° F.)fraction is from about 18-20 wt. % of the total product. If diluentrecycle is employed, once equilibrium is reached in the process, only asmall fraction of the gas conversion naphtha will be needed as makeupfor the bitumen dilution, with the rest sent to further processing foruse in mogas blending.

For maximum diesel production, the 700° F.+ waxy fraction is convertedto hydrocarbons boiling in the middle distillate range. Those skilled inthe art know that hydroisomerizing the 700° F.+ waxy fraction includesmild hydrocracking (c.f., U.S. Pat. No. 6,080,301 in whichhydroisomerizing the 700° F.+ fraction converted 50% to lower boilinghydrocarbons). Thus, if desired all or a portion the higher 700° F.+fraction may be hydrocracked and hydroisomerized to produce additionaldiesel material. The invention will be further understood with referenceto the Figures.

Referring to FIG. 1, a gas conversion plant 10 is located over, adjacentto or proximate to a bitumen production facility 12, which producesbitumen from an underground formation. The produced bitumen is dilutedwith naphtha from 23 and the resulting mixture of bitumen and diluent istransported, via pipeline 22, to a bitumen upgrading facility 14.Production facility 12 comprises an underground tar sand formation andmeans (not shown) for injecting steam down into the formation, pumpingout the softened bitumen, and separating gas and water from the producedbitumen. A methane containing natural gas and air or oxygen arerespectively passed into the gas conversion plant via lines 16 and 18.The gas conversion plant produces synthesis gas, heavy hydrocarbons andlight hydrocarbons, with the light hydrocarbons comprising naphtha andhydrocarbons boiling in the diesel range. It also produces high andmedium pressure steam, water, a tail gas useful as fuel and hydrogen.High pressure steam from the gas conversion plant is passed down intothe tar sand formation via line 20 to stimulate the bitumen production.Naphtha for the bitumen dilution is removed from the gas conversionplant via line 23. A high cetane diesel fraction is removed from the gasconversion plant to line 32, via lines 28 and 30. In the upgradingfacility, the bitumen is upgraded by fractionation, coking andhydrotreating to produce a diesel fraction which is removed and passed,via line 26, to line 30. The higher cetane gas conversion dieselfraction and the lower cetane bitumen diesel mix in 30 to form a mixtureof both diesel fractions. This mixture is passed, via line 32, totankage (not shown) as a diesel stock. Hydrogen for the hydrotreating ispassed into 14 via line 24. Optionally, at least a portion of thenaphtha diluent is recovered from the bitumen in 14 and recycled back toline 23 for dilution, via dashed line 33. Other process streams are notshown for the sake of simplicity.

Turning now to FIG. 2, in this embodiment the gas conversion plant 10comprises a synthesis gas generating unit 32, a hydrocarbon synthesisunit 34 comprising at least one hydrocarbon synthesis reactor (notshown), a heavy hydrocarbon fraction hydroisomerizing unit 36, a dieselfraction hydroisomerizing unit 38, a fractionating column 40 and ahydrogen producing unit 41. Natural gas that has been treated to removeheteroatom compounds, particularly sulfur, and C₂-C₃₊ hydrocarbons, ispassed into the synthesis gas generator 32, via line 42. In a preferredembodiment, the natural gas will have been cryogenically processed toremove nitrogen and CO₂, in addition to the heteroatom compounds andC₂-C₃₊ hydrocarbons. Oxygen or air, and preferably oxygen from an oxygenplant is fed into the synthesis gas generator via line 44. Optionally,water or water vapor is passed into the synthesis gas generator via line46. The hot synthesis gas produced in the generator is cooled byindirect heat exchange (not shown), with water entering the unit vialine 49. This produces high pressure steam, all or a portion of whichmay be passed, via line 50, to the bitumen producing facility tostimulate the bitumen production. The pressure and temperature of thissteam may be as high as 2000/2200 psia and 635/650° F. This steam may befurther heated prior to being used for the bitumen production. The coolsynthesis gas is passed from unit 32 into hydrocarbon synthesis unit 34,via line 48. A slip stream of the synthesis gas is removed via line 52and passed into a hydrogen production unit 41, in which hydrogen isproduced from the gas and passed, via line 54, into the heavyhydrocarbon hydroisomerization unit 36. In unit 41, hydrogen is producedfrom the synthesis gas by one or more of (i) physical separation meanssuch as pressure swing adsorption (PSA), temperature swing adsorption(TSA) and membrane separation, and (ii) chemical means such as a watergas shift reactor. If a shift reactor is used due to insufficientcapacity of the synthesis gas generator, physical separation means willstill be used to separate a pure stream of hydrogen from the shiftreactor gas effluent. Physical separation means for the hydrogenproduction will typically be used to separate the hydrogen from thesynthesis gas, irrespective of whether or not chemical means such as awater gas shift reaction is used, in order to obtain hydrogen of thedesired degree of purity (e.g., preferably at least about 90%). TSA orPSA that use molecular sieves can produce a hydrogen stream of 99+%purity, while membrane separation typically produces at least 80% purehydrogen. In TSA or PSA the CO rich offgas is sometimes referred to asthe adsorption purge gas, while for membrane separation it is oftenreferred to as the non-permeate gas. In a preferred embodiment thesynthesis gas generator produces enough synthesis gas for both thehydrocarbon synthesis reaction and at least a portion of the hydrogenneeded for hydrocarbon production by physical separation means, so thata water gas shift reactor will not be needed. Producing hydrogen fromthe synthesis gas using physical separation means provides relativelypure hydrogen, along with an offgas which comprises a hydrogen depletedand CO rich mixture of H₂ and CO. This CO rich offgas is removed from 41via line 56 and used as fuel or fed into the hydrocarbon synthesis unit34. If feasible, when hydrogen is produced from the synthesis gas, it ispreferred that the mole ratio of the H₂ to CO in the gas be greater thanstoichiometric, with at least a portion of the CO recovered and passedback into line 48, via line 56. It is particularly preferred that theprocess be adjusted so that the CO rich offgas passed back into thehydrocarbon synthesis reactor be sufficient to adjust the H₂ to CO moleratio in the syntheses gas passing into 34 to about stoichiometric. Thisavoids wasting the valuable CO by burning it as fuel. Hydrogenproduction from synthesis gas by one or more of (PSA), (TSA), membraneseparation, or a water gas shift reaction is known and disclosed in U.S.Pat. Nos. 6,043,288 and 6,147,126. In another preferred embodiment, aportion of the separated hydrogen is removed from line 54, via line 58,and passed to one or more of (i) the bitumen upgrading facility if it isclose enough, to provide reaction hydrogen for hydroconversion of thebitumen and particularly hydrotreating of the bitumen diesel fractionand (ii) hydroisomerization unit 38 for mild hydroisomerization of atleast the heavy gas conversion diesel fraction, to reduce its pour pointwith minimal effect on the cetane number, and preferably at least tounit 38. In the hydrocarbon synthesis reaction unit 34, the H₂ and CO inthe synthesis gas react in the presence of a suitable hydrocarbonsynthesis catalyst, preferably one comprising a supported cobaltcatalytic component, to produce hydrocarbons, including a light fractionand a heavy fraction. The synthesis reaction is highly exothermic andthe interior of the reactor must be cooled. This is accomplished by heatexchange means (not shown) such as tubes in the reactor, in whichcooling water maintains the desired reaction temperature. This convertsthe cooling water to medium pressure steam having a pressure andtemperature of, for example, from 150-600 psia and 250-490° F. Thuscooling water enters the unit via line 60, cools the interior of thesynthesis reactor (not shown) and turns to medium pressure steam whichis passed out via line 62. All or a portion of this steam may also beused for bitumen production; for utilities in the gas conversionprocess, for fractionation, etc. If the bitumen upgrading facility isclose enough, all or a portion of this steam may be passed to thebitumen upgrading unit, where it may be used for power generation, tosupply heat for fractionation, to lance coke out of a coker, etc. It ispreferred to heat this medium pressure to a superheat quality, before itis used for bitumen production. The heavy hydrocarbon fraction (e.g.,700° F.+) is removed from 34 via line 74 and passed intohydroisomerization unit 36 in which it is hydroisomerized and mildlyhydrocracked. This converts some of the heavy hydrocarbons into lowerboiling hydrocarbons, including hydrocarbons boiling in the dieselrange. The lighter hydrocarbon fraction (700° F.−) is removed from 34via line 64 and passed into a mild hydroisomerization unit 36. Hydrogenfor the hydroisomerization reaction enters 38 via line 37. This lighterfraction may or may not include the 500° F.− hydrocarbons of the totaldiesel fraction, depending on whether or not it is desired to retain theoxygenates in this fraction (c.f., U.S. Pat. No. 5,689,031). The gaseousproducts of the hydrocarbon synthesis reaction comprise C₂-C₃₊hydrocarbons, including hydrocarbons boiling in the naphtha and lowerdiesel boiling ranges, water vapor, CO₂ and unreacted synthesis gas.This vapor is cooled in one or more stages (not shown), during whichwater and C₂-C₃₊ hydrocarbons condense and are separated from the restof the gas, and passed out of the reactor via line 64. The water iswithdrawn via line 66 and the liquid, light hydrocarbons via line 70.These light hydrocarbons include hydrocarbons boiling in the naphtha anddiesel ranges, and are passed to line 80. The water may be used forcooling, steam generation and the like and, if a plentiful source ofsuitable water is not available, then preferably for at least coolingthe hot synthesis gas to produce high pressure steam for the bitumenproduction. The remaining uncondensed gas comprises mostly methane, CO₂,minor amounts of C³⁻ light hydrocarbons, and unreacted synthesis gas.This gas is removed via line 72 and used as fuel to heat boilers formaking steam for power generation, bitumen stimulation, upgrading, andthe like. All or a portion of the water removed via line 66 may also beheated to make steam for any of these purposes and, if a plentifulsource of suitable water is not available, then preferably for at leastcooling the hot synthesis gas to produce high pressure steam for thebitumen production. The hydroisomerized heavy fraction is removed from36 via line 76 and passed to line 80. The less severely hydroisomerizeddiesel material is removed from 38 via line 78 and passed into line 80,where it mixes with the hydroisomerized heavy fraction. This mixture,along with the condensed light hydrocarbons from line 70 pass intofractionater 40. The fractions produced in 40 include a naphtha fraction82, a diesel fraction 84 and a lube fraction 86. Any C³⁻ hydrocarbonspresent in the fractionater are removed via line 88 and used as fuel.Optionally, all or a portion of the lube fraction may be recycled backinto the hydroisomerizing unit 36 via line 89, in which it is convertedinto hydrocarbons boiling in the diesel range, to increase the overalldiesel production. All or a portion of the naphtha fraction, andpreferably comprising at least a light naphtha fraction, is removed fromthe fractionater via line 82 and passed to the bitumen producingfacility 12, for bitumen dilution.

An embodiment of a bitumen upgrading facility 14 useful in the practiceof the invention is shown in FIG. 3 as comprising an atmospheric pipestill 90, a vacuum fractionater 92, a fluid coker 94, a gas oilhydrotreater 96, a combined naphtha and middle distillate hydrotreater98 and a distillate fractionater 100. Bitumen is passed, via line 22,from the bitumen production facility into atmospheric pipe still 90. Infractionater 90, the lighter 650-750° F.− hydrocarbons are separatedfrom the heavier 650-750° F.+ hydrocarbons and passed, via line 102 tohydrotreater 98. The 650-750° F.+ hydrocarbons are passed to vacuumfractionater 92, via line 104. Optionally, hydrocarbons boiling in thenaphtha boiling range (e.g., the naphtha diluent) may be separated andremoved from 90 via line 91. It may be desirable to remove this naphtha,which is mostly the diluent naphtha, by means of a rough flashfractionater, rather than pass the entire mixture of diluent and bitumeninto 90. In 92, the heavier fraction produced in 90 is separated into a1000° F.− heavy gas oil fraction and a 1000° F.+ bottoms. The bottomsare passed into fluid coker 94, via line 106 and the heavy gas oilfraction passed into gas oil hydrotreater 96, via lines 108 and 110.Fluid coker 94 is a noncatalytic unit in which the 1000° F.+ fractioncontacts hot coke particles, which thermally crack it to lower boilinghydrocarbons and coke. The coke is withdrawn from the bottom of thecoker via line 112. While not shown, this coke is partially combusted toheat it back up to the bitumen cracking temperature of about 900-1100°F. This consumes part of the coke and the remaining hot coke is passedback into the coker, to provide the heat for the thermal cracking. Thelower boiling hydrocarbons produced in the coker comprise naphtha,middle distillates and a heavy gas oil. These lower boilinghydrocarbons, which include the 700° F.− hydrocarbons boiling in thedesired diesel range, are passed, via line 114 and 102, intohydrotreater 98. The 700° F.+ gas oil is passed into gas oilhydrotreater 96, via line 110. Hydrogen or a hydrogen containing treatgas is passed into the hydrotreaters via lines 116 and 118. In thehydrotreaters, the hydrocarbons react with the hydrogen in the presenceof a suitable sulfur and aromatics resistant hydrotreating catalyst, toremove heteroatom (e.g., sulfur and nitrogen) compounds, unsaturatedaromatics and metals. The gas oil fraction contains more of theseundesirable compounds than the distillate fuels fraction and thereforerequires more severe hydrotreating. The hydrotreated gas oil is removedfrom hydrotreater 96 and passed, via line 120, to storage fortransportation or to further upgrading operations. The hydrotreated 700°F.− hydrocarbons pass from hydrotreater 98 into fractionater 100, vialine 122, in which they are separated into light naphtha and dieselfractions. The naphtha is removed via line 124 and the diesel via line126. The higher cetane diesel from the gas conversion facility is passedinto line 126 from line 84 to form a mixture of the two, to produce adiesel fuel stock having a higher cetane number than the bitumen dieselfraction removed from fractionater 100. This blended diesel fuel stockis sent to storage for blending or to further processing into one ormore types of diesel fuel. The hydrotreated naphtha is preferably usedfor mogas.

Hydrocarbon synthesis catalysts are well known and are prepared bycompositing the catalytic metal component(s) with one or more catalyticmetal support components, which may or may not include one or moresuitable zeolite components, by ion exchange, impregnation, incipientwetness, compositing or from a molten salt, to form the catalystprecursor. Such catalysts typically include a composite of at least oneGroup VIII catalytic metal component supported on, or composited with,with at least one inorganic refractory metal oxide support material,such as alumina, amorphous, silica-alumina, zeolites and the like. Theelemental Groups referred to herein are those found in the Sargent-WelchPeriodic Table of the Elements, © 1968 by the Sargent-Welch ScientificCompany. Catalysts comprising a cobalt or cobalt and rhenium catalyticcomponent, particularly when composited with a titania component, areknown for maximizing aliphatic hydrocarbon production from a synthesisgas, while iron catalysts are known to produce higher quantities ofaliphatic unsaturates. These and other hydrocarbon synthesis catalystsand their properties and operating conditions are well known anddiscussed in articles and in patents.

It is understood that various other embodiments and modifications in thepractice of the invention will be apparent to, and can be readily madeby, those skilled in the art without departing from the scope and spiritof the invention described above. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the exactdescription set forth above, but rather that the claims be construed asencompassing all of the features of patentable novelty which reside inthe present invention, including all the features and embodiments whichwould be treated as equivalents thereof by those skilled in the art towhich the invention pertains.

What is claimed is:
 1. A process for producing a diesel fuel fractioncomprising: (i) stimulating the production of bitumen with steamobtained from a hydrocarbon gas-producing process that produces naphthaand diesel fractions and steam in addition to the hydrocarbon gas, (ii)diluting the produced bitumen with naphtha produced by said hydrocarbongas-producing process to form a pipelineable fluid mixture comprisingsaid bitumen and diluent naphtha, (iii) transporting said mixture bypipeline to a bitumen upgrading facility, (iv) upgrading said bitumen tolower boiling hydrocarbons, including a bitumen-produced dieselfraction, and (v) forming a mixture of said hydrocarbon-produced andbitumen-produced diesel fractions.
 2. A process according to claim 1wherein diesel fraction produced by said gas conversion has a cetanenumber higher than that of said diesel fraction produced from saidbitumen.
 3. A process according to claim 2 wherein said steam comprisesat least one of (i) high pressure steam and (ii) medium pressure steam.4. A process according to claim 3 wherein said diesel fraction producedfrom said bitumen to remove heteroatom and unsaturated aromaticcompounds.
 5. A process according to claim 4 wherein said naphthadiluent comprises a light naphtha fraction.
 6. A process according toclaim 5 wherein said bitumen diesel fraction is hydrotreated to reducethe amount of said compounds prior to said mixing.
 7. A processaccording to claim 6 wherein said naphtha diluent is used on aonce-through basis.
 8. A process for producing a diesel fuel fractionfrom bitumen comprises the steps of (i) stimulating the production ofbitumen with steam obtained from a natural gas fed gas conversionprocess that produces naphtha and diesel hydrocarbon fractions andsteam, (ii) treating at least a portion of said gas conversion dieselfraction to reduce its pour point, (iii) diluting said bitumen with saidgas conversion naphtha to form a pipelineable fluid mixture comprisingsaid bitumen and diluent, and transporting said mixture by pipeline to abitumen upgrading facility, (iv) upgrading said bitumen to lower boilinghydrocarbons, including a heteroatom-containing diesel fraction, and (v)treating said bitumen diesel fraction to reduce its heteroatom content,wherein at least a portion of both treated diesel fractions are combinedto form a diesel stock having a cetane number higher than that of thetreated bitumen diesel fraction.
 9. A process according to claim 8wherein at least a portion of both said diesel fractions are blended.10. A process according to claim 9 wherein at least a portion of bothsaid diesel fractions are blended subsequent to said treating.
 11. Aprocess according to claim 10 wherein said blend has a cetane numberhigher than that of said bitumen diesel fraction.
 12. A processaccording to claim 11 wherein said bitumen upgrading comprises cokingand fractionation.
 13. A process according to claim 12 wherein saidtreatments comprise hydroisomerizing said gas conversion diesel fractionand hydrotreating said bitumen diesel fraction.
 14. A process accordingto claim 13 wherein said naphtha diluent is used on a once-throughbasis.
 15. A process according to claim 14 wherein said gas conversionalso produces water and a tail gas useful as fuel used to make steamfrom said water.
 16. A process for producing a diesel fuel fraction frombitumen comprises: (i) converting natural gas to a hot synthesis gascomprising a mixture of H₂ and CO which is cooled by indirect heatexchange with water to produce steam; (ii) contacting said synthesis gaswith a hydrocarbon synthesis catalyst in one or more hydrocarbonsynthesis reactors, at reaction conditions effective for said H₂ and COin said gas to react and produce heat, liquid hydrocarbons includingnaphtha and diesel fuel fractions, and a gas comprising methane andwater vapor; (iii) removing heat from said one or more reactors byindirect heat exchange with water to produce steam; (iv)hydroisomerizing at least a portion of said diesel fraction formed in(ii) to reduce its pour point; (v) passing at least a portion of saidsteam produced in either or both steps (i) and (iii) into tar sand toheat soak and reduce the viscosity of said bitumen; (vi) producing saidbitumen by removing it from said formation; (vii) reducing the viscosityof said produced bitumen by mixing it with a diluent comprising saidnaphtha produced in step (ii); (viii) transporting said mixture bypipeline to a bitumen upgrading facility. (ix) converting said bitumento lower boiling hydrocarbons, including a diesel fuel fractioncontaining heteroatom compounds; (x) hydrotreating said bitumen dieselfuel fraction to reduce its heteroatom content, and (xi) combining atleast a portion of said pour point reduced and hydrotreated diesel fuelfractions.
 17. A process according to claim 16 wherein said combinedfractions comprise a diesel fuel stock having a cetane number higherthan said diesel fraction produced by said bitumen conversion.
 18. Theprocess of claim 1 wherein the hydrocarbon gas-producing process in step(i) is a natural gas conversion process.